Essential idea: The lungs are actively ventilated to ensure that gas exchange can occur passively.

6.4 Gas exchange

By Chris Paine

https://bioknowledgy.weebly.com/

Two processes maintain the concentration gradients between the blood and the alveolar air to ensure that diffusion of both oxygen and carbon dioxide can occur: firstly circulation of the blood brings a constant supply of high carbon dioxide, deoxygenated blood to the alveoli. Secondly the diaphragm (micrograph image) and intercostal muscles constantly increase and decrease the volume of the lungs to cause ventilation to occur, this is turn ensures a supply of high oxygen, low carbon dioxide air to the alveoli. The muscles cause the lungs to increase and decrease in volume by contractions. You can clearly see the striations in the diaphragm muscle tissue above. The striations help the muscle tissue to contract and relax.

http://napavalley.edu/people/bmoore/PublishingImages/Pages/Histology-Page/Diaphragm%20100X.bmp

Understandings

Statement Guidance

6.4.U1

Ventilation maintains concentration gradients of

oxygen and carbon dioxide between air in alveoli

and blood flowing in adjacent capillaries.

6.4.U2 Type I pneumocytes are extremely thin alveolar

cells that are adapted to carry out gas exchange.

6.4.U3

Type II pneumocytes secrete a solution

containing surfactant that creates a moist

surface inside the alveoli to prevent the sides of

the alveolus adhering to each other by reducing

surface tension.

6.4.U4 Air is carried to the lungs in the trachea and

bronchi and then to the alveoli in bronchioles.

Students should be able to draw a diagram to

show the structure of an alveolus and an

adjacent capillary.

6.4.U5

Muscle contractions cause the pressure

changes inside the thorax that force air in and

out of the lungs to ventilate them.

6.4.U6

Different muscles are required for inspiration and

expiration because muscles only do work when

they contract.

Applications and Skills

Statement Guidance

6.4.A1 Causes and consequences of lung cancer.

6.4.A2 Causes and consequences of emphysema.

6.4.A3 External and internal intercostal muscles, and

diaphragm and abdominal muscles as examples

of antagonistic muscle action.

6.4.S1 Monitoring of ventilation in humans at rest and

after mild and vigorous exercise. (Practical 6)

Ventilation can either be monitored by simple

observation and simple apparatus or by data

logging with a spirometer or chest belt and

pressure meter. Ventilation rate and tidal

volume should be measured, but the terms

vital capacity and residual volume are not

expected.

Why do we need a ventilation system? We are large organisms. Oxygen cannot diffuse into all our cells directly from the air, nor can waste products be directly ejected from the body. We have specialised organ systems, which are efficient, but need delivery of nutrients and removal of waste. The ventilation system ensures the blood can be the medium for this.

We are land-borne. Gases need moist surfaces (membranes) in order to diffuse. Our lungs are moist membranes, allowingoxygen to diffuse into the blood and carbon dioxide to diffuse out.

The ventilation system maintains a large concentration gradient between the alveoli and the blood. The constant flow of past the alveoli brings blood with a high CO2 concentration and low O2

concentration. Breathing out keeps the CO2 concentration in the alveoli low, so it diffuses out of the blood. Breathing in keeps O2 concentration in the alveoli high, so it diffuses into the blood.

Diagram from: http://www.sciencequiz.net/jcscience/jcbiology/gapfilling/breathingsystem.htm

http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP15104

http://highered.mheducation.com/sites/0072495855/student_view0/chapter25/animation__gas_exchange_during_respiration.html

6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and

blood flowing in adjacent capillaries.

6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.

Can you use the diagram to produce a flow chart to show the passage of air into the lungs?

6.4.A3 External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic

muscle action. AND 6.4.U5 Muscle contractions cause the pressure changes inside the thorax that force air in and out of

the lungs to ventilate them.

Inspiration Expiration

pressure change decrease in pressure(draws air inwards)

increase in pressure(pushes air outwards)

volume change increase decrease

ribcage movement up and outward down and inward

external intercostal muscles contract relax

internal intercostal muscles relax contract

diaphragm contract(flattens, moves downwards)

relax

abdominal muscles relax contract(pushes the diaphragm up)

diagrams

Summary of the mechanics of ventilation

http://media1.shmoop.com/images/biology/biobook_animalmovement_graphik_36.png

Inspiration Expiration

pressure change decrease in pressure(draws air inwards)

increase in pressure(pushes air outwards)

volume change increase decrease

ribcage movement up and outward down and inward

external intercostal muscles contract relax

internal intercostal muscles relax contract

diaphragm contract(flattens, moves downwards)

relax

abdominal muscles relax contract(pushes the diaphragm up)

diagrams

Summary of the mechanics of ventilation

6.4.A3 External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of

antagonistic muscle action. AND 6.4.U5 Muscle contractions cause the pressure changes inside the thorax that

force air in and out of the lungs to ventilate them.

Micrograph of the lungs – what structures can you identify?

http://neurobio.drexelmed.edu/education/pil/microanatomy/Cases/01_Quintana/4_Epithelium/Images/alveolarepithelium.jpg

Name this structure

Identify this cell type

http://neurobio.drexelmed.edu/education/pil/microanatomy/Cases/01_Quintana/4_Epithelium/Images/alveolarepithelium.jpg

erythrocytes(Red blood cells)

capillary

Micrograph of the lungs – what structures can you identify?

6.4.U2 Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange. AND

6.4.U3 Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli

to prevent the sides of the alveolus adhering to each other by reducing surface tension.

Edited from: https://beyondthedish.files.wordpress.com/2011/11/gas-barrier-small.jpg

http://neurobio.drexelmed.edu/education/pil/microanatomy/Cases/01_Quintana/4_Epithelium/Images/alveolarepithelium.jpg

Connectivetissue

Type I pneumocytes• A Single layer of cells form

the walls of an alveolus• Extremely thin – short

diffusion distance• Permeable – aids diffusion

Type II pneumocytes• Secrete fluid to moisten

the inner surface of the alveolus

Alveoli walls and gas exchange

• Fluid aids diffusion of gases• Fluid contains surfactant to prevent the walls

sticking together – maintains the lumen• Can divide to form Type I pneumocytes – repair

damage

6.4.A2 Causes and consequences of emphysema.

Emphysema

https://commons.wikimedia.org/wiki/File:Blausen_0343_Emphysema.png

The main cause of emphysema is smoking but it can also develop in people with a long history of chest infections. emphysema can also be caused by air pollution. All of which cause an inflammatory response in the lungs.

Symptoms include:• Difficulty breathing• Cough• Loss of appetite• Weight loss

Protease is released by leukocytes (white blood cells) and inflamed lung tissue. The protease breaks downthe connective tissue, such as elastin) of the lungs. This results in the destruction of small airways and alveoli. This results in the formation of large air pockets and the breakdown of capillaries.

Consequently large air pockets have a much lower surface area to volume ratio than the alveoli which causes insufficient ventilation. When combined with the reduced blood supply this in turn means inefficient gas exchange and hence low blood oxygen levels.

Emphysema is not curable, but there are treatments that can help you manage the disease

Review: 1.6.U6 Mutagens, oncogenes and metastasis are involved in the development of primary

and secondary tumours.

Tumours are abnormal growth of tissue that develop at any stage of life in any part of the body. A cancer is a malignant tumour and is named after the part of the body where the cancer (primary tumour) first develops. Use the links to find out:• most common types of cancer• what causes cancer and associated risk factors• how cancer can be treated

http://www.e-learningforkids.org/health/lesson/cancer/

http://www.cancer.gov/cancertopics/types/commoncancers

http://youtu.be/8BJ8_5Gyhg8

http://www.cancerresearchuk.org/cancer-info/cancerandresearch/all-about-cancer/what-is-cancer/

What causes cancer?

6.4.A1 Causes and consequences of lung cancer.

“Lung cancer is the leading cause of death from cancer in the U.S.”http://www.cancer.gov/types/lung

Lung cancer is cancer that starts in the windpipe (trachea), the main airway (bronchus) or the lung tissue.

By far the biggest cause of lung cancer is smoking. It causes more than 8 out of 10 cases (86%) including a small proportion caused by exposure to second hand smoke in non smokers (passive smoking).

Some other things increase lung cancer risk by a small amount:• Exposure to radon (a radioactive) gas• Air pollution• Previous lung disease• A family history of lung cancer• Past cancer treatment• Previous smoking related cancers• Lowered immunity

The symptoms of lung cancer may include:• Being short of breath• Having a cough most of the time• Coughing up phlegm with blood• An ache or pain in the chest or shoulder• Loss of appetite• Tiredness/fatigue• Losing weight

Like most cancers lung cancer, if untreated, will end with death. Because detection of lung cancer is difficult it is often only diagnosed in the later stages. As a consequence only 10% of those diagnosed will survive for 5 years.

Source: http://www.cancerresearchuk.org/about-cancer/type/lung-cancer/

http://spacecoastdaily.com/wp-content/uploads/2014/01/Cigarette-Smoking-is-Mainly-Causes-of-Lung-Cancer.jpg

Nature of science: Obtain evidence for theories - epidemiological studies have contributed to our understanding of the causes of lung cancer. (1.8)

“Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems.” http://www.who.int/topics/epidemiology/en/

However analytical (statistical) studies are used to study causes.

Surveillance/observation and descriptive studies can be used to study distribution.

There are however limitations to epidemiology as an identified correlation does not always indicate causation:

“overweight and obesity are protective factors against lung cancer, especially in current and former smokers”

Nicotine in tobacco suppresses appetite

http://www.npr.org/2011/06/09/137085989/the-skinny-on-smoking-why-nicotine-curbs-appetite

Until lab studies indicate a link it is possible that weight is negatively correlated with tobacco intake.

http://www.ncbi.nlm.nih.gov/pubmed/22777722

Vs.

http://www.umweltbundesamt.de/sites/default/files/medien/376/bilder/gruppe_c_4designersart_fotolia_53367840_m.jpg

6.4.S1 Monitoring of ventilation in humans at rest and after mild and vigorous exercise. (Practical 6)

Monitoring ventilation

https://commons.wikimedia.org/wiki/File:DoingSpirometry.JPG

https://en.wikipedia.org/wiki/File:Lungvolumes_Updated.png

Independent variable: the intensity of exercise

Dependent variable: What measure(s) are you using for ventilation?

What type of exercise? For how long? How will you make sure that individuals exercise similarly?

Frequency of breaths? Spirometer data showing tidal volumes?

Ethical and safety concerns: how are you making sure that the experiment is safe? Are participants aware of the risks? Are you seeking written permission from participants?

: design an investigation, collect and analyse the data

Controlled variables: what are the key factors that need to be measured and kept constant to ensure a fair test?

Data analysis: you should be calculating a rate. For example the count of breaths or tidal volume per unit time (s or min)

Bibliography / Acknowledgments

Bob Smullen